Flashcards in KEY TERMS Deck (22)

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1

## Interference?

### When two (or more) waves superpose/meet at a point - there is a change in overall displacement

2

## Coherent?

### Constant phase difference (between the waves)

3

## Emission line spectra?

### Where each element produces a unique emission line spectrum because of its unique set of energy levels

4

## Continuous spectra?

### All visible frequencies/wavelengths are present (e.g. of a lamp filament)

5

## Absorption line spectra?

### A series of dark spectral lines against the background of a continuous spectrum

6

## Absolute scale of temp?

### A scale for measuring temp based on absolute zero and the triple point of water (the difference between 1K-2K is the same as that of 1-2 degrees Celsius)

7

## Absolute zero?

### The lowest possible temperature - the temperature at which substances have minimum internal energy

8

## Absorption/attenuation coefficient?

### A measure of the absorption of X-ray photons by a substance (m^-1)

9

## Acceleration?

### The rate of change of velocity

10

## Acceleration of free fall?

### The rate of change of velocity of an object falling in a gravitational field (g)

11

## Acoustic impedance?

### The product of the density - of a substance - and the speed of ultra sound in that substance (Z, or Kgm^-2s^-2)

12

## Acoustic/impedance matching?

### The use of two substances with similar acoustic impedance to minimise reflection of ultrasound at the boundary between them

13

## Activity?

### The rate at which nuclei decay/disintergrate in a radioactive source - measured in becquerels/Bq or decays per second

14

## Alpha radiation?

### Ionising radiation consisting of particles made up two protons and two neutrons - a helium nucleus with Q=+2e

15

## Amount of substance?

### A measure of the amount of matter in moles

16

## Ampere?

### Base unit of electric current - the current flowing in two parallel wires in a vacuum 1m apart, so that there is an attractive force of 2.0 x 10^-7 N per metre length of wire

17

## Amplitude?

### The maximum displacement from the equilibrium position (pos or neg)

18

## Angle of incidence?

### The angle between the direction of travel of an incident wave and the normal at a boundary between two media

19

## Angle of reflection?

### The angle between the direction of travel, of a reflected wave, and the normal at a boundary between two media

20

## Angular frequency?

### A quantity used in oscillating motion - it equals the product of 2 x pie x frequency

21

## Angular velocity?

### The rate of change of an angle for an object moving in a circular path

22